Friction element and method of making the same



Nov. 22, 1955 F. LOMBARDY FRICTION ELEMENT AND METHOD OF MAKING THE SAMEFiled Dec. 30, 1952 INVENTOR. Z

ATTORNE Y.

United States Patent Office FRICTION ELEMENT AND METHOD OF MAKING p ITHE SAME I 18 Claims. (Cl. 1 54 81) This invention relates toimprovements in friction ele ments for use as clutch facings and thelike. The invention relates particularlyto clutch facings known in theart as the circular-wound or spiral-wound type.

One object of this invention is to provide a friction element of thetype specified having high hot spin strength, a highly uniformresistance to, and low rate of, Wear over its entire friction faces,even at high temperatures, and a torque level at least comparable toconventional spiralwound facings. It is a further object of theinvention to provide a method of making such a friction facing.

Another object of the invention is the provision of a method ofproducing large-size, warp-free friction discs of the circular-woundtype employing wire-reinforced fiber yarns.

A still further object of the invention is to provide a method of makingfriction discs of the circular-wound type in which the frictioncharacteristics or coefficient of friction of the friction faces of thefinished product may be varied widely by the application of differenttypes of friction treatment at different stages in the production of thedisc and in various combinations.

In making clutch facings it has been found extremely difiicult tosuccessfully employ the circular-winding method for large-size facings,of 15 in diameter and up, where Wire-reinforced yarns in theirconventional, relatively straight form are used. When wire-reinforcedyarns of a conventional typeare Wound in convolutions, as they are inthe circular-winding method, to form discs in this large-size range,warping is frequently encountered in the finished disc, apparentlybecause the straight wire does not permit the yarn or yarns to yieldunder the play of forces that come into effect during the processing ofthe disc; especially during the curing phase. I have found thatby usinga crimped yarn in accordance with the instant invention, this tendencyto warp can be eliminated. This is believed to result from the fact thatthe crimps or corrugations in the yarn impart a yielding characteristicthereto so that the yarn will yield under the forces developed ratherthan cause thedisc to be twisted or warped.

I have also found that by using crimped Wireereinforced fiber yarn inthis circular-wound type of facing I can obtain a finished producthaving the metal and other friction imparting materials distributed morewidely and uniformly over the friction faces than in the case ofconventional facings of this type. This results from the retention in alarge measure of the crimps or corrugations in the finished product, sothat instead of having the wire and fiber arranged as conventionally inregular, even layers defined by the successive convolutions, theconvolutions have generally radial undulations, which produce a somewhatrandom but, in total effect, wide and uniform distribution of the metaland fiber content. Various friction filler materials can be added atdifferent stages in the pro cessingof the discs, as will be describedhereinafter, in which case these materials will be similarly randomlyand more effectively distributed over the friction faces, to

occupy the pattern of voids established by the undulations.

By employing different combinations of binders and filler materials,different friction characteristics can be obtained ance to wear, lowrate of wear, and a favorable torque level.

The inventionwill be more readily understood by reference to thefollowing detailed description and to the drawing, in which:

Fig. 1 is a side view of a crimped composite strand in the form of anundulated tape made up of individual strands of fiber yarn reinforcedwith metallic strands and impregnated with a binder, one of saidindividual strands being separated from the others at one end and shownin detail;

Fig. 2 is a face view of an annulus formed by arranging on a mandrel,shown in cross-section, a composite strand or tape such as shown in Fig.1 in relatively loose convolutions, prior to compression and curing;

Fig. 2a is a view showing the annulus of Fig. 2 in crosssection, withthe mandrel partly in elevation and partly in section.

Fig. 3 is a partial section on a larger scale of the annulus shown inFig. 2 taken on the line 33, looking in the,

direction of the arrows;

Fig. 4 is a partial face view on a larger scale of the final frictionfacing resulting from the further processing of the annulus shown inFigs. 2 and 3; and

Fig. 5 is a partial section of the final facing, taken on the line 4-4.

My invention involves the use of wire-reinforced fiberyarn in theproduction of a friction element, particularly cotton content forstrength, with one strand of wire 2, as shown in Fig. 1. While theresulting individual wire-reinforced fiber strand 3 is exemplary of thetype of yarn that may be employed, other combinations can be used, in

which the number of strands of wire or fiber, or the types of wire orfiber may be varied. The wire may suitably be brass, but other wire orcombinations of wires may be used in place of, or in conjunction with,the brass wire.

In accordance with the preferred method of the invention, a plurality ofstrands of a Wire-reinforced fiber yarn of the type described above areimpregnated with an appropriate binder represented by the stipplingat 4in Fig. 1 (see also Fig. 3), as by running them through. The innpregnating solution may comprise any of the well-known binders such asthermo-setting resins, natural or syn-L a vat containing theimpregnating solution.

thetic rubber, drying oils, or inorganic binders such as calciumsilicate, or combinations of the above, and also friction particles ofmetal, ground hard rubber, orthe like. The impregnated strands are thendried, ashby air drying, and brought together,conveniently by pass ingthem through a ring of appropriate size, in a rela tively loose bundleto form a composite strand, in which the individual strands extendgenerally in the directionof the length of the composite strand.' Thenumberfof individual wire-reinforced strands which are collected to'form the composite strand may vary, depending upon the thickness of thefriction disc that is desired. Suit- Patented Nov. 22, 1.955

A preferred yarn for effectively practicing the instant invention can beobtained by twisting together two strands 1 of asbestos yarn, having asuitable ably 8--16 such impregnated individual strands may be collectedto form the composite strand. Or the impregnating step could be carriedout after the collection of the. individual strands to form thecomposite strand, though not as effectively.

In the preferred and much more simple and satisfactory method, thecrimping of the yarn is carried out after the composite strand is formedto produce an undulated tape, shown generally at 5 in Fig. 1, but theindividual wire-reinforced strands could be crimped after impregnationand drying and before they are collected to formthe composite strand. Itis necessary in any case to perform the crimping step after theimpregnating and drying steps so that the crimps will not flatten outtoo easily in subsequent handling. The crimping operation may beperformed by passing, the composite strand, or the. individual strand,as the casemay be, through two gears in. mesh, or a hemp break, or inany other suitable manner. A preferred number of crimps or corrugationsper unit length has been found to be about five per inch. In order toobtain satisfactory results, the number of corrugations should not bereduced below two per inch.

In the preferred method, a crimped composite strand 5, formed inaccordance with the above, is arranged in convolutions to form a disc orannulus of the desired size, such a disc being shown generally at 6 inFig. 2. This may be done advantageously by first storing lengths of thecrimped impregnated composite strand in its undulated tape form onspools, from which a suitable length of the undulated tape may be drawnand wound upon itself on a mandrel 7 to form the disc 6 having thedesired diameter, with the width of the tape extending generally axiallyof the disc, and the crimps defining generally radially extendingundulations 8 in the convolutions 9. Alternatively, the composite strandmay be fed directly from the crimping operation to the windingoperation. By the selection of the proper number of individualwire-reinforced fiber strands in the formation of the composite strand,only a single composite strand in the crimped tape form need be woundspirally or circularly upon itself to form the disc on the mandrel, I

in order to obtain a level wind or other suitable winding pattern.

However, instead of collecting the impregnated and dried individualwire-reinforced fiber strands to form the composite strand, as describedabove, the wire-reinforced impregnatedand dried individual strands couldbe crimped individuaIly and thereafter wound directly onthe mandrel insubstantially side-by-side spiral or circular fashion, with the crimpsdefining the generally radially extending undulations 8 in theconvolutions 9, the axial thickness of the resulting disc 'or annulusbeing determined by the number of such strands selected.

Care shouldbe exercised in winding either the composite strand or theindividual strands to use enough tension to cause the resulting blanksto stick together, but with as little flattening of the crimps aspossible.

However formed in accordance with the foregoing, the resulting annulusor disc 6 comprises a suitable amount of the selected; crimpedwire-reinforced yarn arranged upon itself in convolutions to form apreform of the desired size in which the crimps or. corrugations in theyarn define the generally radial undulations 8 in the convolutions 9. Asexemplary of the amount of. yarn, that maybe employed, approximately1,000 grams. of impreg nated, crimped, wire-reinforced. fiber yarn wassuccessfully: used in making an FMS 1618 clutch facing having,

. 4 as final dimensions, 16% outside diameter by 10" inside diameter by.135" thick.

After forming the disc or preform of the impregnated, dried and crimpedyarn as described above, the preform may be finished in a number of waysto arrive at a final friction element having a corresponding variety offriction characteristics. Preferably, the preform is placed in a bumpmold and compressed in an axial direction as indicated by the arrows inFig. 3 to provide a densified blank, after which the binder is cured.The compressed and densified blank has characteristics as indicated inthe cross-sectional detail at the left side of Fig. 5. Either before orafter compressing the disc, but before cure, the disc may be redipped inthe impregnating solution, or otherwise impregnated with the sameor adifferent solution, drained, and allowed to dry. As in the firstimpregnating step, various friction imparting filler materials may beadded to the solution, in which case the second impregnation should beperformed before compressing the,

disc. These friction filler materials, as in the first instance, mayinclude metal, hard ground rubber, or other well-known frictionparticles. By selecting different combinations of friction treatmentsfor the first and second impregnating steps, the frictioncharacteristics of the resulting product can be widely varied.

In compressing the impregnated, dried, and crimped preforms, thepreforms are usually reduced in thickness, about a third, as from .260"to .140. The blanks thus formed may be reduced further in thickness to,for example, .125 by grinding after cure.

The cured blanks made in accordance with the above may be finished inany of the usual ways as by subjecting them to baking, grinding,drilling, and counter-boring operations. In the final friction discs, asshown in Figs. 4 and 5, the crimps or corrugations in the yarn arelargely retained, the yarn being disposed in the convolutions 9, inwhich the crimps in the yarn define the generally radial undulations 8.The yarn is held in the disc form in the hard, cured binder matrix,which, as illustrated at 1 0,v fills the spaces surrounding the wire andfiber, it being understood that the binder matrix thus referred toincludes such friction particles as may have been incorporated in. thefriction treatment. (1) content of the yarn is exposed at the frictionsurfaces (the axial end faces) of the disc to render visible at thesesurfaces the generally radial undulations defined in the convolutions bythe crimps or corrugations in the yarn. As a result of the undulations,the exposed fiber and wire content is distributed somewhat randomly butwidely and, in total effect, uniformly over the friction surfaces, andthe remainder of the fiber and wire is similarly distributed in the bodyof the disc in a manner exemplified in Fig. 5. The friction treatment10, filling the spacesbetween the fiber and wire to form the bindermatrix, of course is also very effectively distributed throughout thedisc, including its friction faces, as a result ofithe describeddistribution of the fiber and wire.

Friction discs of. the type described above, and made in accordance withthe describedmethod, which is very simple and economical to practice,have the desirable properties already discussed. It will thus be seenthat the stated objects of my invention have been attained.-

Having thus described my invention in rather full de-; tail, it will beunderstood that these details need not be strictly adhered to and thatvarious changes and modifie cations may suggest themselves to oneskilled in the art, all falling within the scope of the invention asdefined by the subjoined claims.

What I claim is:

' 1. In a method of making a friction element which includes spirallywinding wire-reinforced hardenable. binder impregnated and. dried. fiberyarn inconvolut-ions, the step of crimping. saidyarn after impregnationand dryinghut before winding. 7

2. A method of making a friction element comprising,

Part of the wire (2) and fiber impregnating wire-reinforced fiber yarnwith a binder, drying and crimping the impregnated yarn, arranging adesired quantity of the crimped yarn in convolutions to form a disc ofthe desired size, compressing said disc, and curing the binder.

3. In a method of making a friction element, the steps of impregnatingWire-reinforced fiber yarn with a binder, drying and crimping theimpregnated yarn, arranging a quantity of the crimped yarn inconvolutions having radial undulations defined by the crimps, to form adisc, compressing said disc, and curing the binder.

4. A method of making a friction element comprising impregnatingwire-reinforced fiber yarn with a binder, drying and crimping theimpregnated yarn, arranging a desired quantity of the crimped yarn inconvolutions to form a disc of the desired size, compressing said disc,impregnating said disc with additional binder, and curing the binder.

5. A method of making a friction element comprising, impregnatingwire-reinforced fiber yarn with a binder, drying and crimping theimpregnated yarn, arranging a desired quantity of the crimped yarn inconvolutions to form a disc of the desired size, impregnating said discwith additional binder, compressing said disc, and curing the binder.

6. In a method of making a friction element, the steps of arranging acomposite strand of crimped hardenable binder impregnatedwire-reinforced fiber yarn in convolutions upon itself to form a disc,compressing the disc, and curing the binder.

7. In a method of making a friction element, the steps of forming acomposite strand of hardenable binder impregnated and dried fiber yarnincluding asbestos and wire reinforcement, crimping said compositestrand, arranging said composite strand in convolutions upon itself toform a disc, compressing the disc, and curing the binder.

8. In a method of making a friction element, the steps of forming acomposite strand of hardenable binder impregnated and driedwire-reinforced fiber yarn, in which composite strand the strands ofwire and fiber are bundled together and extend generally in thedirection of the length of the composite strand, crimping said compositestrand to form an undulated tape, arranging said tape in convolutions toform a disc having the undulations in the tape disposed as generallyradial undulations in the convolutions, compressing the disc, and curingthe binder.

9. A method of making a friction element comprising, impregnatingstrands of wire-reinforced fiber yarn with a binder, drying andcollecting together a plurality of said impregnated strands to form acomposite strand, crimping said composite strand, arranging said crimpedcomposite strand in convolutions to form a disc of the desired size,compressing the disc, and curing the binder.

10. A method of making a friction element comprising, impregnatingstrands of yarn including asbestos and wire reinforcement with a binder,drying and collecting together in a bundle a plurality of saidimpregnated strands to form a composite strand in which said impregnatedstrands extend generally in the direction of the length of the compositestrand, crimping said com posite strand to form an undulated tape,arranging said tape in convolutions upon itself to form a disc havingthe undulations in the tape disposed as undulations in the convolutionsand in which the Width of the tape extends generally axially of thedisc, compressing the disc, and curing the binder.

11. In a method of making a friction element, the steps of forming acomposite strand of wire-reinforced fiber yarn, impregnating saidcomposite strand with a binder, drying and crimping the impregnatedcomposite strand, arranging said composite strand in convolutions toform a disc of the desired size, compressing the disc, and curing thebinder.

12. A friction element comprising crimped wire-reinforced fiber yarndisposed in convolutions defining a disc, said yarn being held in theform of said disc by a hard, cured binder matrix.

13. A friction element comprising crimped wire-reinforced fiber yarnarranged in convolutions defining a disc, the crimps in the yarndefining undulations in the convolutions, said yarn being held in theform of said disc by a hard, cured binder matrix.

14. A friction element comprising crimped Wire-reinforced fiber yarnarranged in convolutions defining a disc, the crimps in the yarndefining undulations in the convolutions, said yarn being held in theform of said disc by a hard, cured binder matrix, part of the fiber andwire content of said yarn being exposed at the friction surfaces of thedisc.

15. A friction element comprising crimped yarn including asbestos andwire reinforcement arranged in convolutions defining a disc, said yarnbeing held in the form of said disc by a hard, cured binder matrix, partof the fiber and wire content of said yarn being exposed at the frictionsurfaces of the disc and forming thereat a visible pattern of radialundulations in the convolutions.

16. A friction element comprising corrugated wire-reinforced fiber yarndisposed in convolutions defining a disc, the corrugations in the yarndefining generally radial unduiations in the convolutions, said yarnbeing held in the form of said disc by a hard, cured binder matrix, partof the fiber and wire content of said yarn being exposed at the frictionsurfaces of the disc to render visible thereat the generally radialundulations define-d in the convolu tions by the corrugations in theyarn.

17. In a method of making a friction element, the steps comprisingforming a tape of hardenable binder impregnated and dried fiber strandsincluding wire-reinforcement, crimping said tape, arranging said tape inconvolutions to form a disc, compressing the disc, and curing thebinder.

18. The method defined in claim 17, in which said tape is crimpedtransversely and arranged lengthwise in convolutions to form the disc.

References Cited in the file of this patent UNITED STATES PATENTS1,493,371 Moeller May 6, 1924 1,719,290 Danielson July 2, 1929 2,258,237Bockius et al. Oct. 7, 1941 2,343,930 Rowe Mar. 14, 1944 2,648,618Palumbo Aug. 11, 1953

1. A METHOD OF MAKING A FRICTION ELEMENT COMPRISING, IMPREGNATINGWIRE-REINFORCED FIBER YARN WITH A BINDER, DRYING AND CRIMPING THEIMPREGNATED YARN, ARRANGING A DESIRED QUANTITY OF THE CRIMPED YARN INCONVOLUTIONS TO FORM A DISC OF THE DESIRED SIZE, COMPRESSING SAID DISC,AND CURING THE BINDER.
 12. A FRICTION ELEMENT COMPRISING CRIMPEDWIRE-REINFORCED FIBER YARN DISPOSED IN CONVOLUTIONS DEFINING A DISC,SAID YARN BEING HELD IN THE FORM OF SAID DISC BY A HARD, CURED BINDERMATRIX.